Eastern Sierra Snowpack Summary - Dec 02 2016

Avalanche Advisory published on December 2, 2016 @ 8:29 pm

Issued by
Josh Feinberg - Eastern Sierra Avalanche Center

Avalanche Character 1: Persistent Slab

Persistent Slab avalanches can be triggered days to weeks after the last storm. They often propagate across and beyond terrain features that would otherwise confine Wind and Storm Slab avalanches. In some cases they can be triggered remotely, from low-angle terrain or adjacent slopes. Give yourself a wide safety buffer to address the uncertainty.

A significant weak faceted layer of snow ranging from non-existent to 10cm+ can be found above 9,000’ on NW-N-NE-E facing slopes below the Nov 27th storm snow. This layer of facets has been generally found to be sitting on-top of a thick rain crust. Where it is consistent across a slope, a human triggered avalanche could be possible. If you find yourself on slopes >32 degrees with these aspects, especially above 10,000’, investigate the snowpack for yourself and perform your own stability tests.

Avalanche Character 2: Wind Slab

Wind Slab avalanches release naturally during wind events and can be triggered for up to a week after a wind event. They form in lee and cross-loaded terrain features. Avoid them by sticking to wind sheltered or wind scoured areas.

The 2-3” of light fluffy snow that fell early morning on Dec 2 is of little concern at the moment, except perhaps at high elevations above 10,500’ where moderate NE winds may have blown this snow into small deeper denser deposits that may be sensitive to human triggering. If an avalanche did occur in this situation, it would likely be very small, but it would be of concern if it knocked a person off balance in steep rocky terrain. It is always good practice to keep alert for smooth hollow sounding pillows on slopes >32 degrees that could potentialy be a dangerous windslabs. If loose snow exists that can be blown by the wind, dangerous windslabs can form long after actual snowfall events.

Snowpack Discussion

ESAC welcomes you to the 2016-2017 winter season with our first Snowpack Summary of the season! While it is still very early season with a very shallow snowpack at mid to low elevations, people have been getting out and finding some good turns! Red Cone Bowl on the Mammoth Crest (10,000’) has been seeing quite a bit of daily traffic, and there are a few other locations we have gotten reports that folks who are chomping at the bit have been venturing / adventuring to, namely Bloody Mountain and Virginia Lakes. There have been reports of 1-1.5m of snow above 11,000’ … but the trick is to get up to that level and down from that level safely.

Let’s begin with a brief snowpack history for the season. Two significant storms in mid and late October dropped close to 6” of water each around Mammoth, unfortunately temperatures were high and considerable amounts of rain fell below 10,000’, with periods of rain that reached well over 11,000’. This has resulted in the formation of thick ice crusts that can be found between 9,000’ to 11,000’+. There were reports of some evidence of natural avalanches at upper elevations during these storms. A couple weeks of dry weather followed these storms, which resulted in the development of some weak faceted snow, most notably above the last thick ice crust that formed. Below 9,000’ the snowpack disappeared in most places. Then came the November 27th storm, finally coming in cold, dropping almost 1.5” of water and a foot of snow at the 9000’ level, with considerable wind. Some significant avalanches were triggered on Mammoth Mountain as a result of control efforts by ski patrol that propagated considerable distances. (1.5- 4ft crowns!). These avalanches seemed to have failed in the facet layer above the upper thick rain crust. These storm and wind slabs have likely stabilized considerably since this storm 4 days ago, and the likelihood of human triggering low, but still possible especially with the facet and crust combination that they may be sitting on. Keep an eye out for these at upper elevations on E-N-NW facing slopes. Temperatures have since turned cold, and this morning 2-3” of light fluffy snow fell around Mammoth. Winds increased out of the NE throughout the day, which could have formed some very isolated small new wind deposits at upper elevations that could be sensitive to human triggering, and could be enough to knock a rider off balance in tricky terrain. If you are heading out, take the time to poke around, dig a hole, check-out how that facet layer under the Nov 17th storm snow is doing. As cold conditions continue, these faceted weak layers may become more pronounced.

In general, snow line is even higher south of Mammoth, and snowfall amounts have been lower, making access to skiable and rideable terrain even more difficult.

In Summary, there is snow up in them hills! But it’s quite a ways up in them hills. While there is some avalanche concern, there is greater concern right now due to the low tide skiing and riding conditions with plenty of rocks and stumps and logs just below the surface. If you are venturing out, keep your eyes open and your brain working and be careful not to end your season before it’s barely begun!

*This Snowpack Summary will be updated once conditions change and we receive more snow. Regularly scheduled Snowpack Summaries will begin shortly.

**Don’t Forget to come to our Season Kickoff Event on Saturday! See webpage for details.

This Mountain Weather page will include details once regurlarly scheduled Snowpack Summaries begin. For now, click here to see NOAAs up-to-date weather forecast information. Use the map to zero in on your particular location of interest.

Disclaimer

This snowpack summary applies only to backcountry areas outside established ski area boundaries. This snowpack summary only describes general avalanche conditions and local variations always occur. This snowpack summary expires 24 hours after the posted time unless otherwise noted.

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